Effect of Pressure on the Particle Size Distribution of Espresso Coffee

Abstract

Studies regarding particle size distribution, particularly in espressos are surprisingly few. Particle size distribution (PSD) is a plot that displays the average diameter versus percentage volume of the particles present in a sample. With increased awareness amongst coffee drinkers, a study aiming to report the effects of different pressure on particle size distribution of espresso from four different coffee blends was conducted. The method involved pulling of espresso shots at 7, 9, and 11 bar (or atm) from different coffee blends labeled as MA, CO, AL, and MO. Laser diffraction analysis showed different particle size groupings for each set of extraction pressure. Fine particles are within 1.20 to 28.70 µm. The most abundant particle size is centered at 185.4 µm. The particle size distribution of coffee blends composed of 100% Arabica coffee (AL and MO) but sourced from different locations, showed four similar modes or size ranges centered at 3.523, 13.005, 28.70, and 185.4 µm regardless of the extraction pressure or the coffee source. On the other hand, the coffee blends composed of different ratios of Arabica and Robusta (MA and CO) showed different modes depending on the pressure. This indicates the potential of PSD for characterizing the purity of a coffee blend. The particle size distribution can also give insights as to the sensory attributes of the espresso coffee.